The present invention relates in general to isolation of a direct current (dc) power supply from noise generated by an electrically noisy dc load, such as a dc motor, receiving power from the power supply and, more particularly, to an isolation circuit which also regulates power provided to the load from a dc power supply. While the present invention may be used in a variety of applications including electrically noisy loads such as dc motors, pulsing circuits, switching power supplies, solenoid drivers and the like, it will be described herein with reference to an isolation regulator used to drive a dc fan motor used to cool electrical equipment in a cellular telephone amplifier cabinet for which it is particularly applicable and initially being used wherein it isolates the dc fan motor from a battery system and regulates power provided to the dc fan motor from the battery system.
In a cellular telephone amplifier cabinet, power is provided to circuitry which processes cellular telephone signals by at least amplifying and normally performing other processing of the signals. For reliability, the power is provided by a battery system which has sufficient capacity to maintain the operation of the cabinet equipment for satisfactory periods of time to accommodate most interruptions of alternating current (ac) battery charging power which may occur. For similar reliability considerations, the battery system also provides power to other essential equipment within the cabinet including, for example, one or more dc motors which drive one or more cooling fans within the cabinet. Unfortunately, operation of dc motors produces large ripple currents and resulting ripple voltages. Any dc motor must be isolated from the battery system to reduce the ripple noise as well as other noise which can be generated by the motor and coupled into the battery system. If the isolation is insufficient, the resulting noise on the battery system can interfere with proper processing of the cellular telephone signals.
In the past, a pi filter including a large inductor has been used to isolate a dc fan motor from the battery system. However, due to the large inductance required, the filter is large, heavy and costly to assemble since assembly is manually performed. The filter also limits the size of the motor and the fan since only a defined amount of space is allocated to the fan/filter combination, particularly in existing cabinet designs.
It is apparent that there is a need for an improved arrangement for isolating electrically noisy dc loads, such as dc motors, from dc power supplies, such as battery systems, which arrangement is substantially smaller than currently used filters, comparatively lighter in weight, lower in cost and which lends itself to automated production. Preferably, the improved arrangement would regulate power provided to the noisy loads and would perform additional functions currently performed by components provided in addition to currently used filters. For example in the case of a dc fan motor, alarms could be generated to warn of impending failure of the motor, the temperature of associated electrical equipment cooled by operation of the motor could be monitored and the speed of the motor could be controlled based on the temperature of the cooled equipment.